A Hall device has a broad scope of application and has been used, for example, in a non-contact type rotation detecting sensor for a brushless motor employed with a VTR, CD-ROM drive or the like, and in a current flow measuring apparatus.
A currently proposed Hall device for detecting magnetic field which is particularly employed in a magnetic sensor has a variety of shapes. Those include a rectangular shape and a clover shape, and a rectangular or a Van der Pauw type Hall device is typically used when measuring the polarity, density and mobility of carriers within a conductive sample.
FIG. 1 is a schematic view illustrating a structure of a Hall device which is often used for physics experiments. For enhancing the magnetic field detecting sensitivity, the Hall device is provided with a rectangular magnetometric sensing surface 110 having a distance L between a pair of power terminals and a distance W between a pair of Hall voltage output terminals. The opposed short sides are provided with a power terminal C1111 and a power terminal C2112, respectively. The opposed long sides are provided with a Hall voltage output terminal S1113 and a Hall voltage output terminal S2114, respectively.
For the Hall device for detecting a magnetic field, offset compensation is particularly essential. Thus, such a device known as a symmetry-type Hall device has been mainly employed, which attains offset compensation by alternately exchanging the positions of the power terminals and the Hall voltage output terminals (SCM: Spinning Current Method).
The “symmetry-type Hall device” herein refers to a Hall device which includes a rectangular or substantially cross-shaped magnetometric sensing surface and power terminals and Hall voltage output terminals. One of an opposed pair of the corners or sides of the magnetometric sensing surface is provided with a pair of the power terminals and the other of the pair is provided with another pair of the power terminals. One of the other opposed pair of the corners or sides of the magnetometric sensing surface is provided with a pair of the Hall voltage output terminals and the other of the other pair is provided with another pair of the Hall voltage output terminals. Additionally, the geometrical shape of the Hall device is not altered when the positions of the power terminals and the Hall voltage output terminals are exchanged. In other words, the outline of the symmetry-type Hall device is quadrature-symmetrical with its center.
FIG. 2 illustrates the structure of the symmetry-type Hall device. A rectangular magnetometric sensing surface 120 is equipped with power terminals C1121, C2122 and Hall voltage output terminals S1123, S2124 on its four corners. The power terminals and Hall voltage output terminals are opposed.
This symmetry-type Hall device is one of the most widely used Hall devices for detecting magnetic field due to an extremely simple configuration and an easiness of manufacturing.
Additionally, a cross-shaped Hall device is one of the known symmetry-type Hall devices.
FIG. 3 schematically illustrates a structure of a cross-shaped Hall device created by Popovic et al. Four extensions at a cross-shaped magnetometric sensing surface 130 are provided with power terminals C1131 and C2132, and with Hall voltage output terminals S1133 and S2134, respectively mutually opposed.
When the Hall device is formed on a Si substrate, the terminals and the magnetometric sensing surface of the Hall device are freely structured since fine process on the substrate is easily performed. For example, there are disclosed a vertical type Hall device for detecting magnetic field in a parallel direction to a substrate surface in Japanese Patent Application Publication No. 63-055227 (1988), a lateral type Hall device for detecting magnetic field in a perpendicular direction to a substrate in Japanese Patent Application Laying-open No. 7-249805 (1995), a device which accomplishes offset compensation not by the SCM but by dividing output terminals to connect to an offset compensation circuit in Japanese Patent Application Laying-open No. 11-183579 (1999), and a device provided with a configuration and a circuit for reducing variations in offset and sensitivity in Japanese Patent Application Laying-open No. 7-193297 (1995).
The above symmetry-type Hall devices offer an advantage in that they are capable of attaining offset compensation by the SCM. However, such Hall devices have a drawback of providing low sensitivity to detecting magnetic field compared with a rectangular Hall device.
The Hall voltage produced between two Hall voltage output terminals of a constant-current-drive Hall device depends on its configuration, and is calculated according to the following equation:VH=G·rH·I·BZ/ned  (1)where I, BZ, n, and e represent a current flowing between the power terminals, an applied magnetic flux density, a carrier density, and an unit charge, respectively, and d, G, and rH represent a thickness of layer in which current flows, an geometrical factor, and a Hall scattering factor, respectively.
FIG. 4, which is transferred from R. S. Popovic, “Hall Effect Device”, shows the relationship between the ratio of the distance L between the power terminals to the distance W between the Hall voltage output terminals (L/W ratio) and the geometrical factor G of the rectangular Hall device. The longer the distance L between the power terminals is than the distance W between the Hall voltage output terminals, the larger the geometrical factor G becomes. The geometrical factor G is approximately 1 when L>3W. However, the geometrical factor G is only about 0.6 when L=W, which shows a rectangular shape corresponding to the configuration of the symmetry-type Hall device, depending on the applied magnetic flux density. This means that the symmetry-type rectangular Hall device loses approximately 40% of magnetic field detecting sensitivity due to its shape.